Sound reproducing device



March 15, 1.932.'

F. w. LYLE SOUND REPRODUCING DEVICE Filed Sept. 18, 1929 INVENToR Heder/'m/L/y/e,

ToRNEY Patented Mar. 15, 1932 UNITED STATES 'VANIA PATENT OFF i' FREDERICK-W. LYLE, or WILKINSEURG, PENNSYLVANIA, AssIGNoR. To url aIlae-k HOUSE ELECTRIC a MANUFACTURING COMPANY, A CORPORATICN QE PENNSYL- souNnaErEonUcINe DEVICE Animation nea september 1s, 1929. semi No. 393,405.

My-invention relates to sound-producing devices such asv radio receivers and phonograph reproducers.

It is an obj ect of my invention to supply 5 energy to a sound-producing device from a source of periodic current without causing a hum corresponding to said periodicity.

It is a further object of my invention to provide Aan arrangement in which a filter,

which removes the fluctuation from rectified alternating current less completely than has heretofore been regarded as necessary'in order to eliminate the hum, will sufiice for its removal. l

Vacuum tubes have been energized from alternating-current sources before. One

way of doing this is to insert a rectifier and` a filter between the source and the tubes. If the tubes are in a receiving set or in van amplifier belonging to a sound-producing devlce to avoid producing a hum has hereto.- fore required that the filter be expensive, bulk and heavy. e

W en the hum is incompletely eliminated, the quality of the speech or music is unsatise factory. e l A I propose to supplement a filter, which would otherwise be insuilicient, by impressing upon the voice coil of the loud speaker a '*0 current fluctuation of correctintensit and phase to compensate the fluctuations 1n the magnetic field resulting from the iiuctuations in the filtered current. The force exerted upon the diaphragm beingtheresult of the interaction.' of the current in the voice coil with the field produced by the main coil, 'a fluctuation in one can be offset by a corresponding and opposite 4fluctuation in the other.

It is an object of my invention to obtain from the current fluctuations in the lfield coil corresponding fluctuationsin the potential of the grid of one ormore tubes in the amplifier, thereby controlling the output Current of the amplifier, which passes through the voice coil.

Other objects `of myv invention and details of the construction will be clear rorn the following descrilption and accompanying f drawing in whic The figure is a diagrammatic view of the `apparatus and connections.

The source 1 of alternating current supplies, through a` transformer '2, the current for heating the filament 3 of avacuum tube 4.

This tube is shown as of the type havin an indirectly heated cathode 5, but any o the f expedients for preventing current fluctuations in the filament from producing corre,- sponding fluctuations in the out ut of the tube may be employed instead o the indirectly heated cathode7 if preferred,

The source l-is connected to a rectifying device which, as illustrated, includes rectiiers 7 arranged in the form of a Wheatstone bridge. It is not essential to my invention that this particular arrangement of rectifiers be used. Any rectifying arrangement producingan output from each halt` ,of the alternating-current cycleis `preferable to recti.- frying arrangements yielding van output lfrom only one-half of each cycle, but the half-cycle rectifiers may be used if desired,

The output terminals of the rectifier Vare connected to a filterwhich, as illustrated, *inl cludes an inductor 8in one side of the line and a plurality of condensers 9 acrossthe .1g of line at each terminal of the inductor. A moreJ elaborate filter may be used,`co mp rising several inductors in series, with a condenser in shunt between each inductor; and the, next, but with theinvention herein described, it is believed that a filter comprising only the three reactors illustrated will prove'4 suiiit.-

,cient for all ordinary situations.

The output terminals of the filter are-conf nected to the iield Windingll of a loud speaker of the. electrodynamic type.' The iield winding is in shunt to the plate lcircuit of the vacuum tube 4. This circuit includes 7 the cathode-anode space ofthe tube and, in series therewith, Vthe voice coil 12 of the loud speaker, to which the diaphragm -13 is mechanically connected. The cathode of the 'tube 4 is connected, `at 14, to the main leads from the filter to the field "coil11 and the voice coil 12 is connected, at 15, to the other lead from, the filter to the field coil. Thus, the connections from the filter to the branch points 14 and 15 are a common supply for the field coil and the plate circuit.

a rectangle marked signal source. This is intended to stand for the input coil of a receiving set, the pick-up coil of an electric phonograph or any other source of signalcontrolled current. It may also represent the output of an amplifier by Which the signal energy has been so increased that it will ef- 'fe'ctually control the tube 4. Similarly, the tube represented at 4 may, if preferred, instead of delivering energy directly to the voice coil, deliver energy to the input of an amplifier comprising one or more additional tubes, the last of which delivers energy to the vfoice coil. yWith such additional amplification, the potential delivered by the secondary 18 need not be as great as required in the systemas illustrated.

The primary 21 of the transformer 2O is included in one of the vleads from the filter to the field coil. The coupling in this transformer is rendered adjustable in any desired Way. The adjustable connector 22 which determines what portion of the inductor 18 shall be shunted by the adjustable condenser '23, `provide means for additionalV control of the phase and amplitude of the potential fluctuations on the grid 16.

In the operation of the device, alternating current Yis delivered by; the source 1 andl changed by the transformer 2 to the potential bestl adapted for Vthe filamentary heater 3. The cathode 5 is heated thereby and supplies electrons for the space current in the tube 4.

' The output of the alternating-current y source 1 is also delivered to the rectifier 7 and magnetic field across the air gap in Which the voice coil 12 is located. If the current in the voice coil Were steady, there Would result a corresponding periodic mechanical force, acting upon the diaphragm 13.

l The current in the coil -12 varies in accordance With the signal, but it also varies in accordance Withthe potential impressed upon the grid 16 by the secondary 18 of the transformer 20. This variation of the grid potential is produced by the fluctuations in the .primary 21. The direct current is Without effect upon the secondary 18. e yThe amplitude vof the fluctuation supervposed on the direct current, the tightness of current inthe coil 12 may nothave the cor-V rect phase relation to the fluctuationsfinthe magnetic field in Which this coil isl located. To further control this phase relation, the adjustable condenser 23 is provided. The circuit including a portion of the secondary 18 and the condenser 23 is so designed that its resonance frequency is very different from the frequency of the periodic fluctuation in the primary 21. Overemphasis of the natural frequency of this circuit is thus avoided. l

The changes yin potential upon the grid 16 induced by changes in current in the coil I21 are correlated to the changes in current in the field coil 11 and, therefore, to theV changes in intensity in the magnetic eld in Which the coil 12 is located. The changes in potential upon the grid 16 control the changes in current in the voice coil 12 and, therefore, control the mechanical force upon saidfcoil. The adjustments of the coupling, of the terminal 22 and of the condenser 23 are so chosen that the phase of the changes of current in the coil 12 coincide With that of the changes in the magnetic eld but are opposite n sense.

v The tendency of one change to increase the mechanical force upon the diaphragm is, therefore, compensated by the tendency of the other change to diminish it. Coned adjustment Will make the compensation com- ,105

plete. The force exerted upon the diaphragm is thus made independent of the fluctuations in the current delivered by the filter.V Since the action of the filter makes these fluctuations small compared to vthe magnitude of the direct current,'any difference in Wave form between said fluctuations and the corresponding changes in the'fcurrent in the'voice coil 12 Will produce only very small forces acting upon the diaphragm and, therefore, Will giveqrise to no noticeable hum.

When no signal is impressed from the device 18, there vvill be silence, because the fluctuations in the output of the filter are so "nearly ycompletely compensated that they do not move the diaphragm enough to produce an audible sound. When signals are received fromthe device 18, the change they cause in the output current from the tube 4 is characteristic ofthe signals and will in no Way disturb the compensating action described above.` Consequently, no interference with ,the correct action of the means for preventing hum will arise Vfrom'the presence of signals.

, If extraordinary loud signals are received so that the tube 4 operates beyond the straight-line part of its characteristic, some slight hum might come through which would otherwise be compensated, but this can occur only when the signals are very loud and, therefore, only` when the hum will be completely masked thereby.

Many variations of details of the construction will occur to those skilled in the art and the absence of any specific description thereof herein is not intended as a limitation. The only intended limitations are those required by the prior art or indicated in the claims.

I claim as my invention:

1. In combination, an electrodynamic loud speaker having a field coil and a voice coil, a vacuumtube amplifier having a grid circuit and a plate circuit, a common source of current supply connected to said plate circuit and field coil, the voice coil being in series in said plate circuit and the field coil in shunt thereto and a transformer-coupling said common connection to said grid circuit.

2. In combination, an electrodynamic loud speaker having a eld coil and a voice coil, a vacuum-tube amplifier having a grid circuit and a plate circuit, a common source of current-supply connected to said plate circuit and field coil, the voice coil being in series in said plate circuit and the field coil in shunt thereto and a transformer coupling said common connection to said grid circuit, and means for adjusting the phase relation between the voltage impressed by said transformer upon the grid and the fluctuations in current in said common connection.

3. In combination, an electrodynamic loud I speaker having a field coil and a voice coil, a vacuum-tube amplifier having a grid circuit and a plate circuit, a common source of currentsupply connected to said plate circuit and field coil, the voice coil being in series in said plate circuit and the field coil. in shunt thereto, and a transformer coupling said common connection to said grid circuit, means for adjusting the closeness of said coupling and means for adjusting the phase relation of the voltage impressed by said transformer upon the grid and the iiuctuations in current in said common connection.

In testimony whereof, I have hereunto subscribed my name this 30th day of August,

FREDERICK W. LYLE. 

